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8 March 2014ZrO2-TiO2 thin films and resonators for mid-infrared integrated photonics
Mid-infrared (MIR, 2-6 μm wavelength) transparent metal oxides are attractive materials for planar integrated photonic devices for sensing applications. In this study, we present reactive sputtering deposited ZrO2-TiO2 (ZTO) thin films as a new material candidate for integrated MIR photonics. We demonstrate that amorphous ZTO thin films can be achieved with Ti concentration of 40 at.%. With increasing Ti concentration, the optical band gap decreases monotonically from 4.34 eV to 4.11 eV, while the index of refraction increases from 2.14 to 2.24 at 1 μm wavelength. MIR micro-disk resonators on MgO substrates are demonstrated using Ge23/Sb7S70/Zr0.6Ti0.4O2 strip-loaded waveguides with a loaded quality factor of ~11,000 at 5.2 μm wavelength. By comparing with a reference device of Ge23Sb7S70 resonator on MgO and simulating the optical confinement factors, the ZTO thin film loss is estimated to be below 10 dB/cm. Single mode shallow ridge waveguides with a ridge height of 400 nm and a slab height of 1.7 μm are also demonstrated using ZrO2 thin films on MgO substrates. The low loss, relatively high index of refraction, superior stability and proven CMOS compatibility of ZTO thin films make them highly attractive for MIR integrated photonics.